The present invention generally relates to a digitally controlled ring signal generator and, in particular, relates to such a ring signal generator that is both inexpensive and simplistic in the implementation thereof.
In nearly all digital telephone switching systems, a ring circuit is required for each of many groups of subscriber lines interconnected via a digital switching network. Thus, one of the major costs in providing telecommunication services to a very large number of subscribers is dedicated to the line circuits. In fact, considerable effort is continuously being dedicated to both reducing the cost of such line circuits as well as increasing the number of subscriber lines serviced by each circuit.
In recent years, electronic ringing circuits have been developed. This work has been directed at utilizing modern solid state technology and circuit techniques to reduce power requirements and the physical size of components to increase packing density and thereby provide a less expensive circuit.
One example of this technological trend is made clear in U.S. Pat. No. 4,349,703 entitled, "Programmable Ring Signal Generator" issued Sept. 14, 1982 and assigned to the assignee hereof. The above-identified patent is deemed incorporated herein by reference. Therein a digitally controlled ring signal generator is described wherein each ringing circuit services about thirty different subscribers. The operation of the device described therein depends upon the use of a ring signal reference source having two distinct output signals; i.e. a d.c. biased sine wave and a rectified square wave. From these signals, a high voltage sinusoidal ring signal is reconstructed via high voltage commutating switches. The reconstructed signal is then provided, under the control of a ring supervision circuit, to a subscriber line/trunk.
While such a device significantly reduces the bulk and expense of servicing subscriber line/trunk by eliminating the need for rather bulky transformers it, in itself, is somewhat costly because of the need for high voltage commutating switches.